Betel Nut Chewing Is Strongly Associated With General and Central Obesity in Chinese Male Middle‐aged Adults

Betel nut chewing has been reported to increase the risk of cardiovascular disease and all‐cause mortality. The reason is unclear. In this study, we investigated the association between betel nut chewing and general obesity (BMI ≥25 kg/m²) and central obesity (waist circumference (WC) ≥90 cm). A total of 1,049 male subjects, aged ≥40 years, were recruited from Taichung city in Taiwan in 2004. The relationships between betel nut chewing and general and central obesity were studied by multiple linear and logistic regression analyses. The prevalence of current and former betel nut chewing was 7.0 and 10.5% in our male Taiwanese cohort. Current/former betel nut chewers had a higher prevalence of general and central obesity when compared with individuals who had never chewed betel nut. Adjusted for age, diabetes, hypertension, lipids, smoking, alcohol drinking, physical activity, income, and education level, the odds ratios (ORs; 95% confidence intervals) of general and central obesity among the lower consumption of betel nut chewers were 1.78 (1.07, 2.96) and 1.19 (0.70, 2.02), respectively, compared to 2.01 (1.18, 3.41) and 1.89 (1.10, 3.23), respectively, among higher consumption chewers compared to individuals who had never chewed betel nut. The increasing ORs of general and central obesity with higher betel nut consumption revealed dose–response effects. Using multiple linear regression analyses, after adjusting for potential confounders, betel nut consumption was statistically significantly associated with BMI and WC. In conclusion, betel nut chewing was independently associated with general and central obesity in Taiwanese men. Dose–response effects of the association between betel nut consumption and general obesity as well as central obesity were found.     

Trends in tobacco consumption and incidences of associated neoplasms in Papua New Guinea.

From 1960 to 1979 total annual consumption of tobacco in Papua New Guinea increased from 573 to 1800 metric tonnes. The annual consumption of tobacco per head increased from 2.78 to 6.14 kg, and the proportion of commercial cigarettes smoked is estimated to have increased from 20% to 71% of the total tobacco consumption. Between 1965 and 1979 the average annual age standardised incidence of reported cases of carcinoma of the oral cavity increased significantly in women (p less than 0.01) but not in men (p greater than 0.05). This rise might have been related to increasing consumption of tobacco or alcohol, or both, in individuals who habitually chewed betel nut. There was no significant change in the reported incidences of carcinoma of the larynx, lung, oesophagus, pancreas, kidney, or bladder. At present there are no constraints on the marketing of tobacco in Papua New Guinea.     

Evaluation of frequency of micronucleated oral mucosa cells as a marker for genotoxic damage in chewers of betel quid with or without tobacco.

The frequency of micronucleated cells (MNC) derived from exfoliated human oral mucosal cells has been measured to assess genotoxic damage in chewers of betel quid with tobacco (BQT) and tobacco with lime (T). Significantly elevated frequencies of MNC were observed in the exposed groups (BQT = 4.83 +/- 0.70; T = 5.20 +/- 0.66 per 1000 cells) compared to the control group (C = 2.59 +/- 0.37) although the levels observed were lower than those reported in the literature. No correlation was seen between age, duration and frequency of habits and the frequency of MNC in the 2 habit groups. Clastogenic agents in betel quid possibly involved in micronucleus formation are discussed.     

Epidemiology of areca (betel) nut use in the mariana islands: Findings from the University of Guam/University of Hawai`i cancer center partnership program

BackgroundAreca (betel) nut is considered a Group 1 human carcinogen shown to be associated with other chronic diseases in addition to cancer. This paper describes the areca (betel) nut chewing trend in Guam, and health behaviors of chewers in Guam and Saipan.MethodsThe areca (betel) nut module in the Guam Behavioral Risk Factor Surveillance Survey was used to calculate the 5-year (2011–2015) chewing trend. To assess the association between areca (betel) nut chewing and health risks in the Mariana Islands, a cross-section of 300 chewers, ≥18 years old, were recruited from households in Guam and Saipan. Self-reported socio-demographics, oral health behaviors, chronic disease status, diet, and physical activity were collected. Anthropometry was measured. Only areca (betel) nut-specific and demographic information were collected from youth chewers in the household.ResultsThe 5-year areca (betel) nut chewing prevalence in Guam was 11% and increased among Non-Chamorros, primarily other Micronesians, from 2011 (7%) to 2015 (13%). In the household survey, most adult chewers (46%) preferred areca nut with betel leaf, slaked lime, and tobacco. Most youth chewers (48%) preferred areca nut only. Common adult chronic conditions included diabetes (14%), hypertension (26%), and obesity (58%).ConclusionThe 5-year areca (betel) nut chewing prevalence in Guam is comparable to the world estimate (10–20%), though rising among Non-Chamorros. Adult and youth chewers may be at an increased risk for oral cancer. Adult chewers have an increased risk of other chronic health conditions. Cancer prevention and intervention strategies should incorporate all aspects of health.     

The Role of Physical Activity in Harm Reduction among Betel Quid Chewers from a Prospective Cohort of 419,378 Individuals

ObjectiveTo assess the benefits of regular exercise in reducing harms associated with betel quid (BQ) chewing.MethodsThe study cohort, 419,378 individuals, participated in a medical screening program between 1994 and 2008, with 38,324 male and 1,495 female chewers, who consumed 5–15 quids of BQ a day. Physical activity of each individual, based on “MET-hour/week”, was classified as “inactive” or “active”, where activity started from a daily 15 minutes/day or more of brisk walking (≥3.75 MET-hour/week). Hazard ratios for mortality and remaining years in life expectancy were calculated.ResultsNearly one fifth (18.7%) of men, but only 0.7% of women were chewers. Chewers had a 10-fold increase in oral cancer risk; and a 2-3-fold increase in mortality from lung, esophagus and liver cancer, cardiovascular disease, and diabetes, with doubling of all-cause mortality. More than half of chewers were physically inactive (59%). Physical activity was beneficial for chewers, with a reduction of all-cause mortality by 19%. Inactive chewers had their lifespan shortened by 6.3 years, compared to non-chewers, but being active, chewers improved their health by gaining 2.5 years. The improvement, however, fell short of offsetting the harms from chewing.ConclusionsChewers had serious health consequences, but being physically active, chewers could mitigate some of these adverse effects, and extend life expectancy by 2.5 years and reduce mortality by one fifth. Encouraging exercise, in addition to quitting chewing, remains the best advice for 1.5 million chewers in Taiwan.     

Areca (betel) nut chewing practices of adults and health behaviors of their children in the Freely Associated States,Micronesia: Findings from the Children’s Healthy Living (CHL) Program

BackgroundChewing areca (betel) nut has been deemed carcinogenic. The practice has become a public health concern in Micronesia. The Children's Healthy Living (CHL) Program included an areca (betel) nut questionnaire in a survey of household characteristics in the Freely Associated States (FAS). This paper describes areca (betel) nut chewing practices of adults and the health behaviors of their children.MethodsA cross-section of 1200 children (2–8 year-olds) and their caregivers in Chuuk, Kosrae, Pohnpei, Republic of Palau, Republic of the Marshall Islands (RMI), and Yap were recruited. Socio-demographics, adult areca (betel) nut chewing practices, and other health behaviors of children and adults were assessed. Child anthropometric measurements were collected to estimate weight status.ResultsThe FAS areca (betel) nut chewing prevalence was 42%, ranging from 3% (RMI) to 94% (Yap). Among chewers, 84% added tobacco, 97% added slaked lime, 85% added betel leaf, and 24% mixed the components with alcohol. Among FAS children, 95% practiced daily teeth-brushing and 53% visited the dentist annually. Compared to non-chewing households, areca (betel) nut chewing households were more likely to have very young children enrolled, more highly educated adults, and members that used tobacco and alcohol.ConclusionThe FAS areca (betel) nut chewing prevalence (42%) is above the world prevalence of 10–20%, with wide variability across the islands. The oral health findings in this study may inform future oral cancer prevention programs or policies. Regular monitoring of areca (betel) nut use is needed to measure the impact of such programs or policies.     

Formation of reactive oxygen species and of 8-hydroxydeoxyguanosine in DNA in vitro with betel quid ingredients

The formation of reactive oxygen species (ROS) from betel quid ingredients, namely areca nut, catechu and tobacco, was studied using a chemiluminescence (CL) technique. Aqueous extracts of areca nut and catechu were capable of generating superoxide anion and hydrogen peroxide at pH greater than 9.5. The formation of O2 was enhanced by Fe2+, Fe3+ and Cu2+ but inhibited by Mn2+. Tobacco extract failed to generate ROS under similar conditions. Saliva was found to inhibit both O2 and H2O2 formation from betel quid ingredients. Upon incubation of DNA at alkaline pH with areca nut extract and Fe3+ or catechu, 8-hydroxydeoxyguanosine was formed as quantified by high performance liquid chromatography (HPLC)/electrochemical detection. The data suggest a possible role of reactive oxygen species in the etiology of oral cancer in betel quid chewers.     

Bioassay and attributes of a growth factor associated with crown gall tumors

An improved bioassay is described for a factor that promotes tumor growth which was first obtained from extracts of pinto bean leaves with crown gall tumors. Sixteen primary pinto bean leaves per sample are inoculated with sufficient Agrobacterium tumefaciens to initiate about 5 to 10 tumors per leaf and treated with tumor growth factor at day 3 after inoculation. The diameters of 30 to 48 round tumors (no more than 3 randomly selected per leaf) are measured per test sample at day 6. Mean tumor diameter increased linearly with the logarithm of the concentration of tumor growth factor applied. The tumor growth factor was separated by column chromatography from an ultraviolet light-absorbing compound previously reported to be associated with fractions having maximal tumor growth factor activity. Partly purified tumor growth factor showed no activity in a cytokinin bioassay or an auxin bioassay, and negligible activity in gibberellin bioassays. Representatives of these three classes of growth factors did not promote tumor growth. Extracts from crown gall tumors on primary pinto bean leaves, primary castor bean leaves, Bryophyllum leaves, carrot root slices, and tobacco stems showed tumor growth factor activity, whereas extracts from healthy control tissues did not. Extracts from actively growing parts of healthy pinto beans, Bryophyllum, and tobacco, however, showed tumor growth factor activity. Tumor growth factor is proposed to be a normal plant growth factor associated with rapidly growing tissues. Its synthesis may be activated in nongrowing tissues by infection with Agrobacterium sp.     

Accumulation of mitochondrial DNA deletions in human oral tissues -- effects of betel quid chewing and oral cancer

Accumulation of mitochondrial DNA (mtDNA) mutations in human tissues has been associated with intrinsic aging and environmental insult. Recently, mtDNA mutations have been detected in various tumors, including head and neck tumors. However, the factors affecting the occurrence and accumulation of mtDNA deletions in tumor tissues are poorly understood. In Taiwan, betel quid chewing is a major risk factor for oral cancer. Using polymerase chain reaction (PCR) techniques, we examined large-scale deletions of mtDNA in 53 pairs of tumor and non-tumor oral tissues from the patients with or without betel quid chewing history. The results revealed that irrespective of the history of betel quid chewing, the incidences of the 4977bp deletion and other deletions of mtDNA were lower in the tumor portion as compared with the non-tumor portion. The average proportions of the 4977bp deleted mtDNA in the tumor tissues of the betel quid chewers and non-betel quid chewers were 13- and 5-fold, respectively, lower than those in the corresponding non-tumor tissues. Moreover, the average proportion of 4977bp deleted mtDNA was significantly higher (P<0.05) in the non-tumor oral tissues of the patients with betel quid chewing history than that of the patients without the history of betel quid chewing. These results suggest that betel quid chewing may increase mtDNA mutation in human oral tissues and that accumulation of mtDNA deletions and subsequent cytoplasmic segregation of these mutations during cell division could be an important contributor to the early phase of oral carcinogenesis.     

Protective effect of hydroxychavicol, a phenolic component of betel leaf, against the tobacco-specific carcinogens

The phenolic compound, hydroxychavicol (HC), present in betel leaf, was synthesized and tested for its antimutagenic effect against the mutagenicity of the 2 tobacco-specific N-nitrosamines (TSNA), N′-nitrosonornicotine (NNN) and 4-(nitrosomethylamino)-1-(3-pyridyl)-1-butanone (NNK), in 2 different test systems, viz. the Ames Salmonella/microsome assay and the micronucleus test using Swiss male mice. We are reporting the synthesis of HC of a high degree of purity. We observed that HC suppressed the mutagenic effects of NNN and NNK in both test systems used. These results indicate that HC may have a role to play in reducing the risk of oral cancer in betel quid with tobacco chewers.     

Analysis of cytogenetic effects in bone-marrow cells of rats subchronically exposed to smoke from cigarettes which burn or only heat tobacco

The genotoxic effects of 90-day nose-only exposures to smoke from new cigarettes, which heat but do not burn tobacco (New), or from reference cigarettes, which burn tobacco, were evaluated in Sprague-Dawley rats by examining the cytogenetic endpoints of sister-chromatid exchanges (SCE), chromosome aberrations, and micronuclei in bone-marrow cells. The concentrations of wet total particulate matter (WTPM) and carbon monoxide in the smoke from both cigarette types were similar. The mainstream smoke from both New and reference cigarettes was adjusted to WTPM concentrations of approx. 200 and 400 μg/1 for low and high smoke exposure. Rats were exposed to smoke 1 h per day, 5 days per week for 13 consecutive weeks. Inhalation of smoke by the exposed animals was confirmed by analysis of blood carboxyhemoglobin and plasma nicotine. Examination of bone-marrow cells following the final day of exposure showed that smoke from neither the New nor reference cigarette induced a positive response in the SCE, chromosome aberration, or micronucleus assays in rats.     

Associations between oral hygiene habits,diet, tobacco and alcohol and risk of oral cancer: A case–control study from India

ObjectiveThis study examines the association between the incidence of oral cancer in India and oral hygiene habits, diet, chewing and smoking tobacco, and drinking alcohol. We also assessed the effects of oral hygiene habits with oral cancer risk among chewers versus never chewers.MethodsA hospital-based case–control study was conducted in Pune, India, based on face-to-face interviews, anthropometry, and intra-oral examinations conducted for 187 oral cancer cases and 240 controls.ResultsPoor oral hygiene score was associated with a significant risk of oral cancer (adjusted OR = 6.98; 95%CI 3.72–13.05). When stratified by tobacco-chewing habit, the poor oral hygiene score was a significant risk factor only among ever tobacco chewers (adjusted OR = 14.74; 95%CI 6.49–33.46) compared with never chewers (adjusted OR = 0.71; 95%CI 0.14–3.63). Dental check-ups only at the time of pain by ever-chewers with poor oral hygiene was associated with an elevated risk (adjusted OR = 4.22; 95%CI 2.44–7.29), while consumption of green, yellow, and cruciferous vegetables and citrus fruits was protective. A linear dose–response association was observed between oral cancer and chewing tobacco in terms of age at initiation, duration, and frequency of chewing per day (P < 0.001). Smoking more than 10 bidis/cigarettes per day (adjusted OR = 2.74; 95%CI 1.28–5.89) and for a duration >25 years (adjusted OR = 2.31; 95%CI 1.14–4.71) elevated the risk of oral cancer.ConclusionGood oral hygiene habits – as characterized by healthy gums, brushing more than once daily, use of toothpaste, annual dental check-ups, and a minimal number of missing teeth – can reduce the risk of oral cancer significantly. In addition to refraining from chewing/smoking tobacco, a diet adequate in fruits and vegetables may protect against the disease.     

SOME EFFECTS OF VIRUS INFECTION ON LEAF WATER CONTENTS OF NICOTIANA SPECIES

Infection with tobacco mosaic virus decreases the water content which detached tobacco leaves attain when kept for 20 hr. in conditions of minimum water stress, and does so more when the plants are kept in light before inoculation than when they are kept in darkness. No such effects of infection during the first day after inoculation were obtained with tobacco leaves infected with either tobacco etch virus or potato virus X , or with Nicotiana glutinosa leaves infected with tobacco mosaic virus. These results, like those showing early effects of TMV on respiration and photosynthesis of tobacco leaves, suggest that inoculation with TMV affects deeper leaf tissues than the epidermis earlier in tobacco leaves than in other leaves, and earlier than other viruses in tobacco leaves.     

Influence of smokeless tobacco exposure on detoxification status and chromosomal damage in male and female habitues

In India, a large number of tobacco chewers and masheri users are chronically exposed to tobacco genotoxicants. Detoxification processes involving cellular glutathione (GSH) and glutathione S-transferases (GST) determine the outcome of exposure to environmental mutagens including those present in tobacco. Hence, in this study, GSH levels, GST activity, GSTM1 genotype and cytogenetic damage were determined using lymphocytes from 114 smokeless tobacco habitues and controls. The study groups comprised of male tobacco chewers, female masheri users, and age- and sex-matched controls. Irrespective of the tobacco habit, GSH levels and GST activity were higher in females than in males. In both the groups of habitues, GSH levels were similar to those in controls, while a significant reduction in GST activity was observed in tobacco chewers only. The frequency of cytogenetic alterations was significantly elevated in both the groups of habitues with respect to controls. However, break-type aberrations were more frequent in tobacco chewers while gaps were commonly observed in masheri users. Differences in the nature of chromosomal alterations in the two groups of habitues appeared to be related to variation in total tobacco exposure and gender-related differences in the efficacy of the GSH/GST detoxification system.     

Mitochondrial DNA Copy Number and Risk of Oral Cancer: A Report from Northeast India

Background

Oral squamous cell carcinoma (OSCC) is the sixth most common cancer globally. Tobacco consumption and HPV infection, both are the major risk factor for the development of oral cancer and causes mitochondrial dysfunction. Genetic polymorphisms in xenobiotic-metabolizing enzymes modify the effect of environmental exposures, thereby playing a significant role in gene–environment interactions and hence contributing to the individual susceptibility to cancer. Here, we have investigated the association of tobacco - betel quid chewing, HPV infection, GSTM1-GSTT1 null genotypes, and tumour stages with mitochondrial DNA (mtDNA) content variation in oral cancer patients.

Methodology/Principal Findings

The study comprised of 124 cases of OSCC and 140 control subjects to PCR based detection was done for high-risk HPV using a consensus primer and multiplex PCR was done for detection of GSTM1-GSTT1 polymorphism. A comparative ΔCt method was used for determination of mtDNA content. The risk of OSCC increased with the ceased mtDNA copy number (P_trend = 0.003). The association between mtDNA copy number and OSCC risk was evident among tobacco – betel quid chewers rather than tobacco – betel quid non chewers; the interaction between mtDNA copy number and tobacco – betel quid was significant (P = 0.0005). Significant difference was observed between GSTM1 - GSTT1 null genotypes (P = 0.04, P = 0.001 respectively) and HPV infection (P<0.001) with mtDNA content variation in cases and controls. Positive correlation was found with decrease in mtDNA content with the increase in tumour stages (P<0.001). We are reporting for the first time the association of HPV infection and GSTM1-GSTT1 null genotypes with mtDNA content in OSCC.

Conclusion

Our results indicate that the mtDNA content in tumour tissues changes with tumour stage and tobacco-betel quid chewing habits while low levels of mtDNA content suggests invasive thereby serving as a biomarker in detection of OSCC.     

Effects on sister chromatid exchange frequency of polymorphisms in DNA repair gene XRCC1 in smokers

The association between metabolic polymorphisms and cigarette smoking-induced cancers has been documented. However, the role of DNA repair polymorphism in carcinogenesis is less clear. To investigate if the polymorphisms of metabolic traits and DNA repair modulate smoking-related DNA damage, we used sister chromatid exchange (SCE) as a marker of genetic damage to explore the relationship of microsomal epoxide hydrolase (mEH), glutathione S-transferase M1 (GSTM1), and X-ray cross-complementing group 1 (XRCC1) and cigarette smoking-induced SCE. Sixty-one workers without significant exposure to mutagens were recruited. Questionnaires were completed to obtain detailed occupational, smoking, and medical histories. SCE frequency in peripheral lymphocytes was determined using a standard cytogenetic assay and GSTM1, mEH (exons 3 and 4), XRCC1 (codon 399) genotypes were determined using polymerase chain reaction-restriction fragment length polymorphism (PCR/RFLP). Smokers had higher SCE frequency than non-smokers (8.4 versus 7.1, P<0.05). Among workers who had smoked equal to or greater than 10 cigarettes each day, those with XRCC1 Arg/Gln+Gln/Gln had higher SCE frequency than those with XRCC1 Arg/Arg after adjusting for potential confounders (9.0 versus 7.9, P<0.05). The interaction of XRCC1 and cigarettes smoked per day on SCE frequency was also observed (P=0.02). There was no significant interaction between cigarettes smoked per day with GSTM1 and mEH on SCE frequency. Our results support previous epidemiological studies that XRCC1 may play a role in cigarette smoking-induced lung cancer.     

Oral microflora in betel-chewing adults of the Karen tribe in Thailand

ObjectiveTo study a possible influence of betel chewing on the composition of the oral microflora in plaque and saliva and on oral health parameters as well as a possible betel effect on oral bacteria in vitro.Material and methodsThirty-two adults (16 betel chewers and 16 non-betel-chewing controls) of the Karen Hill tribe in Thailand were investigated. Saliva samples and 2 pooled supragingival plaque samples were taken from each individual for microbial analysis with culture and 4 subgingival samples for analysis with the DNA–DNA hybridization method against 12 periodontitis associated bacterial species. Caries (DMFS), plaque (PlI%) and bleeding on probing (% BoP) was registered as well as number of sites with >5 mm probing pocket depth (PPD). Water extract of the betel (areca chatechu) nut was tested for its antimicrobial effect in vitro against 10 oral bacterial species with the agar diffusion method.ResultsAn antimicrobial effect of betel nut water extract was found on the oral microorganisms in vitro. The levels of mutans streptococci and lactobacilli in saliva were low or absent in both chewers and controls. The prevalence of the periodontitis associated bacteria was >90%. Betel chewers had significantly lower levels of some bacteria in subgingival plaque (Prevotella intermedia p < 0.001) than non-chewers. This study population was low in missing teeth (mean 0.7 and 0.3), caries decay (DS 2.1 vs 1.6), and number of deep pockets (mean 1.9 vs 1.3). Great variation in oral hygiene (PlI and BoP) between the subjects was seen.ConclusionsAn antimicrobial effect of the betel nut was found in vitro and with a possible effect also in vivo however it did not seem to influence clinical parameters such as plaque index, caries prevalence (DMFS), bleeding on probing and number of deep pockets.     

Use of Smokeless Tobacco by Indian Women Aged 18–40 Years during Pregnancy and Reproductive Years

Objectives

This paper discusses patterns of daily smokeless tobacco (SLT) use and correlates of poly SLT use among married women aged 18–40 years in a Mumbai slum community with implications for tobacco control.

Methods

Using a mixed methods approach, the study included a structured survey with 409 daily SLT users and in-depth interviews with 42 women. Participants for the survey were selected using a systematic sampling procedure (one woman in every fourth eligible household). Univariate and bivariate analysis, and multiple logistic regressions were conducted to identify demographic and social factors associated with women’s use of poly SLT products. To illustrate survey results, in-depth interviews were analyzed using Atlas ti software.

Results

Sixty-four percent of the women surveyed used only one type of SLT; of these, 30% used mishri, 32% used pan with tobacco and the rest used chewed tobacco (11%), gul (17%) or gutkha (10%). Thirty-six percent used more than one type of SLT. Poly SLT users chewed or rubbed 50% more tobacco as compared to single users (mean consumption of tobacco per day: 9.54 vs. 6.49 grams; p<0.001). Women were more likely to be poly SLT users if they were illiterate as compared to literate (adjusted odds ratio [AOR]=1.67; 95% confidence interval [CI]=1.07-2.71), if they had lived in Mumbai for 10 years or more, versus less than ten years (AOR=1.67, 95% CI=1.03-2.71); and if their husband was a poly SLT user as compared to a non SLT user (AOR=2.78, 95% CI=1.63-4.76). No differences were noted between pregnant and non-pregnant women in SLT consumption patterns.

Conclusions

Tobacco control policies and programs must focus specifically on both social context and use patterns to address SLT use among women of reproductive age with special attention to poly SLT users, an understudied and vulnerable population.     

Distribution of the frequency of sister chromatid exchange among Leningrad inhabitants

Peculiarities of frequency variations in sister chromatid exchanges (SCE) were studied in a group of healthy Leningrad citizens who are not engaged in health-risk industries. No relations were found between the SCE frequency and sex, age and smoking habit (10 cigarettes per day as much). The statistical processing of the data obtained was made taking into account the errors in individual measurements of the SCE frequency. Repeated measurements revealed systematic and statistically significant variations in the rate of SCE.     

Variation in the human lymphocyte sister-chromatid exchange frequency: results of a long-term longitudinal study

The variation in lymphocyte sister-chromatid exchange (SCE) frequency as a function of time was investigated in nonsmokers and smokers. The smokers were divided into 3 groups depending on their smoking status. The group termed 'smokers' participated in a program to stop smoking but did not reduce or eliminate their use of tobacco; 'smoke enders' successfully completed the smokending program and remained free of tobacco for the duration of the study, while the 'variable' group stopped smoking for a limited time but then resumed smoking. 8 or more blood samples per person were obtained over a period of at least 12 months. The SCE frequencies for each of these groups were compared with each other and with those of two previous longitudinal study groups from our laboratory. The proportion of high-frequency cells (HFCs) was also determined for each sample. The results confirm our previous finding that SCE frequencies and the proportion of HFCs observed in separate samples from the same individual are more likely to be different as the time between samples increases. We also show that smokers have significantly more SCEs and HFCs than do nonsmokers, that SCE frequencies in smokers do not decline for at least 12 months when smoking is stopped, and that among smokers, significant seasonal variation in the SCE frequency occurs. These results provide useful information concerning the effects of smoking upon SCE frequencies, and will be helpful in designing and interpreting the results of long-term human population cytogenetic studies.